Fusarium Head Blight (Scab) Risk, Fungicide Selection and Fungicide Timing

 Risk

Fusarium head blight risk increases in the northern portion of the Red River Valley through the weekend (Figure 1). Most of the state received rain over the past couple of days, and parts of the state will receive more rain in the coming days. The precipitation in combination with the forecasted higher relative humidity values is increasing scab risk in the state.  A marked difference in the risk of infection exists between highly susceptible and moderately resistant varieties (Figure 2).

Fungicide Selection

The most effective fungicides for Fusarium head blight are Miravis Ace®, Prosaro®, Prosaro Pro®, and Sphaerex®. These fungicides on average will provide 45-60% suppression (sometimes higher) and have an efficacy score of “good”.  Tebuconazole (Folicur generics) is considered a “fair” fungicide and provides 20-25% suppression.  Always follow label directions when choosing a fungicide to suppress Fusarium head blight and heed the pre-harvest interval (PHI) and maximum use rates.  

Fungicide Timing

The best time to apply a fungicide for scab and deoxynivalenol (DON) suppression in spring wheat and durum is when the majority of the main stems are at early flowering and up to 7 days after (Figure 3). You can still get some scab suppression if fungicides are applied on full-headed wheat, but not as much if applied at early flowering and up to 7 days later. The best time to apply a fungicide in barley is when a majority of the main stems are at complete full-head emergence and up to 7 days later (Figure 4). In barley, it is critical to wait until at least full-head emergence as you will get very poor fungicide coverage and poor scab suppression on heads that are half-head or only showing awns.

Figure 1. Fusarium head blight risk for very susceptible varieties for June 20 through 24. Darker orange indicates moderate risk and red indicates high risk

Figure 2. Fusarium head blight risk for moderately resistant varieties for June 20 through 24. Darker orange indicates moderate risk and red indicates high risk.

Figure 3. The smaller yellow arrow highlights a spring wheat head at early flowering and points to the small yellow anthers. The longer yellow arrow demonstrates the most effective growth stages to suppress FHB and DON in wheat.

Figure 4. The smaller yellow arrow highlights a barley head at full head. The longer yellow arrow demonstrates the most effective growth stages to suppress FHB and DON in barley.

Andrew Friskop – NDSU Cereal Extension Plant Pathologist

Jochum Wiersma – University of Minnesota Small Grains Extension Specialist